A reader asked: "There are many, many academic bloggers out there feverishly blogging about their areas of interest. Still, there are many, many more academics who don't. So, why do you blog and how does blogging help with your research?"
Good question, simple answer: "Much like other bloggers of any orientation, background and intention I have deep seated need for attention."
There are some other reasons, of course.

"So, why do you blog..."

This is one of the best parts of my actual job because I get to talk with the Boss, who is also my client. You know, the US Taxpayer.

I started into post-baccalaureate education with the motivation of becoming a college professor with my vision almost exclusively the classroom instruction part of the career. I thought I wanted to explain interesting things about my favored "-ology" to fresh-faced undergraduates, year after year. As it happens, my job category doesn't include a great deal of undergraduate instruction. So I think part of the answer to why I blog is that this represents an outlet for those educational drives. Which, apparently, never went away.
The second motivation within this point is a bit more complex. First, I think that since the US taxpayer is paying for this research, s/he should have access to it. I'm not all that into the whole Open Access movement with respect to making scientific papers freely available. Not that I am against it; I'm just not that exercised about this issue yet. Nevertheless, part of my motivation for blogging is to give the Boss a report on what we are collectively doing with the cash. Related to this is a motivation to convince the Boss to continue to support the efforts of the biomedical science community. It is no shocker that we are in one of the periodic down-turns in NIH funding levels associated with Congressional priorities moving elsewhere. While these trends are indeed cyclical, the up-cycle doesn't happen by magic. It happens because of a concentrated effort on many fronts to (re)convince the public and their Congressional representatives that the NIH is a GoodThing. A good investment in our collective future. Instead of merely contenting myself with sending letters to my members of Congress (and getting rapidly put on the "issue wackaloon" list, btw) I hope to reach a somewhat broader swath of people. Hopefully sometimes they will be motivated to dash off a note to their own members of Congress.
Finally, I have two relatively specific motivations which drive two of my most-frequent topics of discussion. I started blogging on WordPress in February of 2007 with posts on careerism in the NIH-funded biomedical science game and posts on popular-press treatment of MDMA-related science and the science-denialism in the Wikipedia entry on MDMA. To the extent that I have specific goal-related motivations in my blogging these remain good examples.
In what I term my "science careerism" posts, I discuss any manner of things that I think I have learned the hard way, or other trainees/young scientists typically learn the hard way. Some of my experiences may be of use to Readers and the discussions that ensue often cover many different perspectives. These topics range from nontraditional job seeking, to careerist tactics and strategies to specific NIH grant-seeking advice and beyond. I also have selfish motivations in that I have many issues with respect to my own career that I feel can be improved by increasing the direct involvement of younger scientists in directing the course of the "system". Younger and transitioning scientists typically leave these tasks to the older, more experienced scientists- is it any surprise that things are tilted in the benefit of the older scientists? So I blog to convince younger scientists to become more involved with issues of career at an earlier stage.
The posts that I write on specific scientific issues are nearly always focused on drug abuse topics. For one thing, the Boss usually finds this area of science to be of interest and it is easy to engage with people in conversation. People feel as though they have opinions to offer in a way that they would not for discussions of, say, the electrical firing properties of a subset of cortical cells when the brain is trying to determine the color and shape of an object crossing the visual field. People have more familiarity with drug abuse and are interested in offering anecdotes and viewpoints. I like that. For another thing, this is an area where the science denialists come a-calling. I don't think I need to belabor the point for the ScienceBlogs audience but suffice it to say that there are many people that are highly motivated to question the validity of the process of science. I happen to think that this is a very bad trend that has somewhat dangerous implications for our collective future. In my domain, the denialists typically argue "There is nothing wrong with smoking a little dope or taking a little MDMA now and again and the science that shows otherwise is all just a conspiracy by the Man". So by blogging on topics of drug abuse, I have a chance to defend the process of science in my specific sub-area.

"...and how does blogging help your research?"

I don't know that it does.
Of course, like many of the activities in which we engage as scientists there are often undefinable and nebulous benefits accruing for which we have very little proof of benefit until later. Some of this can be in codifying one's own thinking on a topic through the process of writing a blog entry. It can be through the discussions that result, both with other scientists and with the lay-readership. Occasionally I find that reading blogs helps me in a specific way by bringing papers to my attention that I would otherwise perhaps not have noticed. This is more a benefit of being engaged in the blogosphere; being a reader of blogs would perhaps suffice for this purpose.
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Update 06/17/08: Others are getting into the theme including RNA Underworld and the NatureNetwork bloggers here and here.
[h/t: Bora]